/Engine/Plugins/Experimental/GeometryScripting/Source/GeometryScriptingCore/Public/GeometryScript/MeshPolygroupFunctions.h
if the mesh is not Triangle-Compact (eg GetHasTriangleIDGaps == false) then the returned list will also have the same gaps
static [UDynamicMesh](API\Runtime\GeometryFramework\UDynamicMesh) * GetAllTrianglePolygroupIDs ( [UDynamicMesh](API\Runtime\GeometryFramework\UDynamicMesh) * TargetMesh, [FGeometryScriptGroupLayer](API\Plugins\GeometryScriptingCore\GeometryScript\FGeometryScriptGroupLayer) GroupLayer, [FGeometryScriptIndexList](API\Plugins\GeometryScriptingCore\GeometryScript\FGeometryScriptIndexList) & PolygroupIDsOut )